In Vivo Micropuncture Section: 1. Simultaneous determination of pH, pCO2 and total CO2 concentration in the rat renal cortex during control conditions and various states of acid-base imbalance. 2. Effects of glucose on bicarbonate reabsorption in the rat proximal convoluted tubule. 3. Effect of PTH and cyclic AMP on bicarbonate reabsorption in the rat proximal convoluted tubule. 4. Determine whether there exists a chloride/bicarbonate exchange mechanism in the proximal tubule. 5. Direct determination of pH and pCO2 in the rabbit proximal and distal tubule. In Vitro Microperfusion Section: 1. Examination of the effect of potassium on hydrogen secretion across the collecting duct. 2. Determine whether and how aldosterone effects Na and Cl transport across the thick ascending limb of Henle. 3. Examine whether the juxtamedullary proximal tubule reabsorbs bicarbonate by the same mechanisms as the superficial proximal tubule.